The sliding contact arrangement is disposed to produce an electrical connection between an electrical connecting line and a slip ring on the spindle, said slip ring rotating during the operation of the erosion arrangement. The spindle has a tool receptacle that is electrically coupled with the slip ring. In doing so, a current transfer from a voltage source or current source can be accomplished—via the connecting line, the sliding contact arrangement and the slip ring—to the erosion tool that can be driven in a rotating manner.
In electric motors or for current transfer, sliding contact arrangements of this type represent a part that rotates about a rotational axis, said part being embodied as a carbon brush. Such a carbon brush has been known from DE 10 2005 013 106 A1 and is used, for example in washing machine motors. The carbon brush is configured as a multi-layer carbon brush.
As a rule, carbon brushes are pressed by means of an appropriate carbon brush holder with a mechanically and/or pneumatically generated spring force against the rotating slip ring in order to prevent the carbon brush from being lifted off the slip ring. For example, DE 20 2004 014 936 U1 discloses a carbon brush holder.
It has been found, however, that the carbon brushes used until now are not suitable for the current transfer in machine tools and, in particular, in erosion machines. Machine breakdowns and machine down-times occur again and again, because there is no longer a sufficient current transfer by the carbon brushes to the rotating spindle. Considering, in particular, erosion machines such as rotary erosion machines, the sliding contact arrangement is subjected not only to a mechanical load. The sliding contact arrangement and the erosion arrangement in accordance with the invention are intended for use in combined erosion and grinding machines. Considering these, there is the problem that the fluid used for cooling during the grinding operation is used, at the same time, as the dielectric fluid during the erosion process, and thus the fluid may contain grinding particles such as particles of the workpiece that is being machined. Despite purification devices such as filters it is not possible to remove all contaminants from the fluid. The dielectric fluid used for erosion, shavings and the like may enter between the sliding contact arrangement and the slip ring and impair proper contacting. Erosion damage on the slip ring or on the sliding contact arrangement is a frequent occurrence during operation.
In searching for a remedy, two paths have been taken so far. On the one hand, in electrical rotary erosion machines, the electrical connection between the current source or voltage source and the erosion tool was implemented by a line that extends along the rotational axis inside the spindle. There, it is possible to implement the sliding contact connections that do not come into contact with the dielectric medium, shavings or other contaminants. On the other hand, it has been suggested to protect the slip ring and the sliding contact arrangement against the entry of fluids, shavings or the like. However, the encapsulation required therefor is complex and expensive.
In both cases, it is necessary to retrofit erosion machines that are currently commercially available; however, due to machine features, this is at times not possible at all.